Substances

A person can also experience a psychotic episode if they suddenly stop drinking alcohol or taking drugs after using them for a long time. This is known as withdrawal.

It's also possible to experience psychosis after drinking large amounts of alcohol or if you're high on drugs.

Drugs known to trigger psychotic episodes include:

cocaine

amphetamine (speed)

methamphetamine (crystal meth)

mephedrone (MCAT or miaow)

MDMA (ecstasy)

cannabis

LSD (acid)

psilocybins (magic mushrooms)

ketamine

In rare situations, psychosis can also occur as a side effect of some types of medication or as a result of an overdose of that medication.

For example, levodopa, a medication used to treat Parkinson's disease, can sometimes cause psychotic episodes. However, any medicine that acts on the brain can cause psychosis with an overdose.

Never stop taking a prescribed medication unless advised to do so by your GP or another qualified healthcare professional responsible for your care.

See your GP if you're experiencing psychotic side effects caused by medication.

The brain

There's been a great deal of research into how psychosis affects the brain and how changes in the brain can trigger symptoms of psychosis.

Grey matter

Research has revealed several physical and biological changes occur in the brain during a psychotic episode. Grey matter is the part of the brain responsible for processing thoughts.

The results of magnetic resonance imaging (MRI) scans have shown some people with a history of psychosis have less grey matter than most other people. However, it's not yet fully understood why this is.

Dopamine

Researchers also believe dopamine plays an important role in psychosis.

Dopamine is a neurotransmitter, one of many chemicals the brain uses to transmit information from one brain cell to another. It is associated with how we feel whether something is significant, important, or interesting.

It's thought levels of dopamine in the brain become too high in people with psychosis. The excess dopamine interrupts specific pathways in the brain that are responsible for some of its most important functions, such as:

memory

emotion

social behaviour

self-awareness

Disruption to these important brain functions may explain the symptoms of psychosis.

Evidence for the role of dopamine in psychosis comes from several sources, including brain scans and the fact medications known to reduce the effects of dopamine in the brain also reduce the symptoms of psychosis.

However, illegal drugs known to increase levels of dopamine in the brain – such as cannabis, cocaine and amphetamines – can trigger psychosis.

Cannabis: real stories

Please enable JavaScript in order to view the video.

Smoking cannabis can lead to cannabis psychosis, causing you to lose touch with reality. Two men describe how it happened to them.